JP4100920B2 - Plasma processing method and plasma processing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma processing method and a plasma processing apparatus using a capacitively coupled plasma source, and more particularly, a high-quality thin film in a large area by suppressing generation of high-energy electrons in plasma and controlling electron energy low. The present invention relates to a plasma processing method and a plasma processing apparatus for realizing deposition and highly accurate etching.
[0002]
[Prior art]
Capacitively coupled plasma sources with two plate electrodes installed in parallel are used in many plasma processing methods and plasma processing equipment because of their simplicity, but the energy of electrons generated by the generation of plasma is reduced. There was a problem that almost no control was possible from the outside.
[0003]
Therefore, in plasma processing using a capacitively coupled plasma source, the generation of high-energy electrons cannot be suppressed, and high-quality thin film deposition and high-precision etching are performed by high-dissociation radicals generated from high-energy electrons. It was difficult to do.
[0004]
For example, in amorphous silicon thin film deposition by plasma CVD using SiH ₄ , when the density of SiH ₂ that is a high dissociated radical is larger than the density of SiH ₃ that is a low dissociated radical in the plasma, In some cases, the electrical characteristics deteriorated and a thin film with large photodegradation was formed.
[0005]
Further, in the etching of the SiO ₂ film formed on the Si substrate, the low dissociated radical CF ₂ forms a protective film on the exposed Si substrate after the etching of the SiO ₂ film, but the high dissociated radical F Since etching is performed up to the Si substrate, the etching selectivity may be lowered.
[0006]
Conventionally, as a technique for suppressing the generation of high energy electrons and controlling the electron energy to be low, there has been a method of first selecting a plasma source. For example, many high-energy electrons are generated in a capacitively coupled plasma source, an inductively coupled plasma source, and an ECR plasma source, and are generally used in a surface wave plasma source, a microwave plasma source, and a VHF excitation capacitively coupled plasma source. In addition, the electron energy can be controlled to be low. However, in this method, much effort is required to change the plasma source, and the plasma source may not be changed due to restrictions on the manufacturing process. Further, in recent years, with the increase in the size of the processing substrate, a technique for generating plasma uniformly over a large area has been demanded. However, inductively coupled and ECR plasma sources are not suitable for this.
[0007]
In T. Mieno and S. Samukawa, Proc. Of 12th Symp. Plasma Process Sendai, 5 (1995), there is a technology to create an afterglow state by temporally modulating the RF power incident on the plasma source to dissipate electron energy. It is disclosed. However, in this technique, the electron energy is reduced as a time average value, but immediately after the pulse is turned on, high energy electrons are generated and a highly dissociated radical is generated. In some cases, highly dissociated radicals remained.
[0008]
K.Kato.et.al., Appl.Phys.Lett.65,816 (1994) discloses a technique for allowing electrons extracted from a remote plasma to pass through the grid and reducing the energy using the potential difference. Yes. However, this technique has a problem that the plasma source is slow and the plasma processing speed is slow because the electron source is lowered on the substrate on which the film is deposited because the plasma source and the film forming chamber are separated from each other, and the amount of radicals generated is reduced.
[0009]
Japanese Patent Application Laid-Open No. 2000-223299 utilizes the property that the llama radius in the cyclotron motion becomes larger as the higher energy electrons, and the high energy electrons extracted from the plasma source collide with the vessel wall and disappear, thereby causing the plasma source A technique for selecting the energy of electrons extracted from is disclosed. In JP-A-3-6203, a filter that selects electrons by passing electrons between electrodes provided with an electrostatic field and changing the trajectory of the electrons by the electrostatic field is applied to the plasma source. Technology is disclosed. However, all of these techniques are applied only to a plasma source having a small area, and a special mechanism including a power source and a magnetic field source has to be newly added.
[0010]
[Problems to be solved by the invention]
In view of the above circumstances, the present invention provides a plasma processing method and plasma processing apparatus using a capacitively coupled plasma source, which suppresses the generation of high energy electrons in the plasma and controls the electron energy to a low area. An object of the present invention is to provide a plasma processing method and a plasma processing apparatus that realize high-quality thin film deposition and high-precision etching.
[0011]
[Means for Solving the Problems]
In the plasma processing method using a capacitively coupled plasma source, the present invention estimates the electron energy and / or high energy electron density in the center of the plasma and the electron energy and / or high energy electron density in the vicinity of the plasma sheath. Injecting fine particles whose amount is controlled based on the estimation into the plasma causes the fine particles to float in the vicinity of the plasma sheath, thereby reducing the rate of statistical heating in the vicinity of the plasma sheath relative to the rate of resistance heating in the center of the plasma. The plasma processing method is characterized in that the plasma processing is performed using the generated plasma and the fine particles are removed before or after the plasma processing is stopped.
[0014]
In the plasma treatment method of the present invention, at least one kind of fine particles selected from the group consisting of resin, glass, Si polycrystal, carbon graphite, and diamond can be used as the fine particles. In the plasma processing method of the present invention, the mass of the fine particles is preferably 10 ⁻¹⁸ to 10 ⁻¹² g. Moreover, in the plasma processing method of this invention, it is preferable that the particle size of microparticles | fine-particles is 0.01-1 micrometer. In the plasma processing method of the present invention, the electron energy and / or the high energy electron density can be estimated from the plasma emission amount.
[0015]
The present invention also provides means for generating plasma by a capacitively coupled plasma source, means for injecting fine particles into the plasma, means for estimating electron energy and / or high energy electron density in the plasma center, and plasma sheath A plasma processing apparatus comprising: means for estimating electron energy and / or high energy electron density in the vicinity; means for controlling the amount of fine particles charged based on the estimation; and means for removing fine particles. And In the plasma processing apparatus of the present invention, as means for estimating the electron energy and / or high energy electron density in the plasma central part, means for measuring the amount of plasma emission in the plasma central part can be used. As a means for estimating the electron energy and / or high energy electron density, a means for measuring the amount of plasma emission in the vicinity of the plasma sheath can be used. In the plasma processing apparatus of the present invention, a pair of opposed electrodes may be provided as means for generating plasma by a capacitively coupled plasma source, and a fine particle removing means may be provided between the electrodes.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0018]
(Capacitively coupled plasma source)
A capacitively coupled plasma source is used in the plasma processing method and plasma processing apparatus of the present invention. When a capacitively coupled plasma source is used, plasma processing can be performed in a large area, which can cope with the recent trend of increasing the area of a substrate. Here, the capacitively coupled plasma source refers to a plasma source that generates plasma by setting two plate electrodes in parallel, grounding one electrode, and applying a high frequency to the other electrode.
[0019]
(Fine particles)
Fine particles are introduced into the plasma generated by the capacitively coupled plasma source. Examples of the fine particles include resins such as acrylic, glass, Si polycrystal, carbon graphite, diamond, and the like, and preferably Si polycrystal and diamond. One type of fine particles may be input, or two or more types of fine particles may be input.
[0020]
The fine particles adsorb electrons in the plasma and behave as giant negative ions. When the fine particles are injected into the plasma, the fine particles act as electron absorption edges near the plasma sheath. Fixed movement makes the movement of electrons extremely slow. Therefore, statistical heating that generates high energy electrons is suppressed.
[0021]
The mass of the fine particles is preferably 10 ⁻¹⁸ to 10 ⁻¹² g, and more preferably 10 ⁻¹⁵ to 10 ⁻¹⁴ g. This is because the fine particles easily float near the plasma sheath.
[0022]
Further, the particle diameter of the fine particles is preferably 0.01 to 1 μm, and more preferably 0.05 to 0.1 μm. This is because more electrons are adsorbed on the fine particles and the movement of the electrons is slowed down. The electrostatic force received when a charged particle is placed in an electric field is proportional to the charge Q of the charged particle, and the acceleration of the charged particle received by the electrostatic force is inversely proportional to the mass m of the charged particle. It can be considered that the index is the charge mass ratio Q / m. For example, fine particles having the above particle diameter adsorb about 10 ⁴ to 10 ⁵ electrons. Therefore, the charge mass ratio Q / m of the fine particles is about 1/10 ⁵ to 1/10 ^{4 as} compared with that of electrons, and the electrons near the plasma sheath hardly move.
[0023]
Means for introducing the fine particles into the plasma includes, for example, by vibrating a tank filled with the fine particles, or by opening and closing a door of the tank filled with the fine particles.
[0024]
(Change in ratio of statistical heating and resistance heating)
There are two types of heating mechanisms in the capacitively coupled plasma source: statistical heating in the vicinity of the plasma sheath and resistance heating in the plasma center. This is described in M. Lieberman and A. Lichtenberg, Principle of Plasma Discharges and Material Processing, JOHN WILEY & SONS, INC (1994) and the like.
[0025]
Since statistical heating is collisionless in its heating mechanism, it generates high-energy electrons that are non-Maxwell distribution. On the other hand, since resistance heating requires collision in its heating mechanism, it generates low-temperature electrons along the Maxwell distribution. Therefore, in order to suppress high-energy electrons, the rate of statistical heating in the vicinity of the plasma sheath may be reduced and the rate of resistance heating in the plasma center may be increased.
[0026]
In the plasma processing method and plasma processing apparatus of the present invention, the rate of statistical heating in the vicinity of the plasma sheath relative to the rate of resistance heating in the center of the plasma is relatively reduced by introducing fine particles to reduce the mobility of electrons. Let For example, when the fine particles are introduced at about 10 ⁴ cm ⁻³ , the density of electrons adsorbed on the fine particles is almost the same as the electron density existing in the plasma before the fine particles are charged. That is, statistical heating can be suppressed by fixing and binding most mobile electrons to the introduced fine particles. That is, high-quality plasma treatment is possible by suppressing the generation of high-energy electrons and thus high-dissociation radicals.
[0027]
(Measurement of electron energy and high energy electron density)
The capacitively coupled plasma source can be provided with means for measuring electron energy, high energy electron density, or both. Preferably, a means capable of measuring the electron energy and high energy electron density in the vicinity of the plasma sheath and in the center of the plasma is installed. By comparing these two electron energies and high energy electron densities, it can be clearly determined that the density of high energy electrons and the average electron energy in the vicinity of the plasma sheath are reduced.
[0028]
Conventionally known measuring means can be used as means for measuring electron energy and high energy electron density. A plasma emission measurement method is preferred in which the plasma emission spectrum is detected by a detection means such as a photodiode. Since the light emission amount of plasma has a positive correlation with the electron energy and the high energy electron density, the increase and decrease of the electron energy and the high energy electron density become clear.
[0029]
Moreover, it is preferable to provide means for calculating information obtained by measuring electron energy and high energy electron density. Further, it is more preferable that a means capable of estimating the statistical heating rate and the resistance heating rate by this calculation is provided. Further, it is more preferable to provide means capable of controlling, preferably feedback controlling, the amount of fine particles charged based on this estimation.
[0030]
(Removal of fine particles floating in the plasma sheath)
The capacitively coupled plasma source is preferably provided with means for removing fine particles suspended in the plasma sheath. This is because it is conceivable that the fine particles are deposited on the substrate to deteriorate the product yield. As a mechanism for removing the fine particles floating on the plasma sheath, a mechanism using electrostatic force acting on the fine particles, a mechanism using the viscous force of the gas flow, and the like are conceivable. For example, an electrostatic probe as shown in WO 01/01467 A1 can be installed. Here, the removal of the fine particles is preferably performed after the plasma is stopped, and the removal time is 5 to 120 seconds, preferably 10 to 50 seconds.
[0031]
(Application of plasma processing method and plasma processing apparatus of the present invention)
The plasma processing method and plasma processing apparatus of the present invention described above can be applied to conventionally known plasma processing. For example, the present invention can be applied to thin film deposition in a manufacturing process such as a solar cell, dry etching in a manufacturing process such as a semiconductor light emitting element.
[0032]
【Example】
(Outline of apparatuses used in Examples and Comparative Examples)
FIG. 1 shows a plasma CVD apparatus used for thin film deposition in Examples and Comparative Examples. In FIG. 1, the outer wall of the deposition chamber 13 is made of stainless steel and is electrically grounded, and an anode electrode 14 and a cathode electrode 15 are disposed inside the deposition chamber 13 so as to face each other. Between the anode electrode 14 and the cathode electrode 15, a ring-shaped fine particle collecting electrode 27 is provided.
[0033]
Here, a substrate holder 12 made of a conductive material sandwiching the substrate 11 is installed on the anode electrode 14, and a heater (not shown) for temperature adjustment is installed. The cathode electrode 15 is connected to a high-frequency power source 16 via a matching line 17 via a coaxial line, and is electrically insulated from the outer wall of the deposition chamber 13. The alignment adjuster 17 adjusts so that the input power is consumed to the maximum extent within the deposition chamber 13 during the particulate deposition. Further, a hole is formed inside the ring of the ring-shaped fine particle collecting electrode 27, and by applying a positive bias to the ring-shaped fine particle collecting electrode 27 to the ring-shaped electrode, fine particles charged to a negative charge can be removed. It can be guided to the hole inside the ring and removed.
[0034]
The material gas is introduced into the deposition chamber 13 from a gas introduction hole 20 provided in the outer wall of the deposition chamber 13 through a pipe connected to a gas cylinder (not shown) installed outside the deposition chamber 13. Further, an exhaust mechanism (not shown) for evacuating the inside of the deposition chamber 13 is connected, and the amount of gas discharged from the gas exhaust hole 21 is adjusted so that the internal pressure of the deposition chamber 13 becomes a desired value. The
[0035]
A transparent quartz window 22 is provided on the side of the deposition chamber 13 so that the inside of the deposition chamber 13 can be observed. Two photodiodes 23 and 24 are provided outside the chamber through the window 22. The photodiode 23 observes the plasma central portion, and the photodiode 24 observes the plasma sheath portion. The output current of the photodiode is input to the current calculator 25, and is compared with the set value. A signal is sent to the vibration generator 26 directly connected to the fine particle tank 19 until the current of the photodiode 24 decreases to the set value. The vibration generator 26 applies vibration to the particle tank 19, and the particles in the particle tank 19 are introduced into the plasma through the inlet 18.
[0036]
(Production and physical properties of examples)
Hereinafter, the amorphous silicon deposition method of this embodiment will be described. First, a substrate 11 made of glass with a 5 cm square and a thickness of 1.1 mm is sandwiched between stainless steel substrate holders 12 and conveyed into the deposition chamber 13. Next, the substrate holder 12 is placed on the anode electrode 14, and the inside of the deposition chamber 13 is depressurized to about 10 ⁻⁵ Pa.
[0037]
Then, 10 SCCM of SiH ₄ and 10 SCCM of H ₂ are introduced from the gas introduction hole 20 as source gases, and the gas exhaust amount is adjusted by the gas exhaust hole 21 so that the pressure is 13 Pa. The temperature of the substrate 11 is set to 200 ° C., and when a high frequency of 13.56 MHz is supplied to the cathode electrode 15 by the high frequency power supply 16, discharge occurs and plasma is generated. Here, the input power was 30 W.
[0038]
Next, simultaneously with the generation of plasma, quartz fine particles having a diameter of 0.1 microns were put into the plasma, and deposition was continued for 30 minutes. Thereafter, a bias was applied to the ring-shaped fine particle collecting electrode 27 for 30 seconds to remove fine particles floating in the sheath, and then the plasma was stopped.
[0039]
Here, with the photodiodes 23 and 24, the time change of the plasma emission intensity near the plasma center and the plasma sheath was measured. The result is shown in FIG. In FIG. 2, the higher the plasma emission intensity, the higher the density of high-energy electrons, which means higher average electron energy.
[0040]
As shown in FIG. 2, there is no temporal change in the plasma emission intensity even after the introduction of the fine particles in the central part of the plasma. This means that there is no change in power incidence due to resistance heating that occurs mainly in the plasma center, that is, there is no change in the density and electron energy of high-energy electrons.
[0041]
On the other hand, in the vicinity of the plasma sheath, when about 5 × 10 ⁴ particles were introduced 10 seconds after the plasma was turned on, the plasma emission intensity was reduced to about 1/5 after the plasma was turned on for 100 seconds. This means that the power incident due to statistical heating mainly generated in the vicinity of the plasma sheath is reduced by the introduction of fine particles, and the density and electron energy of high-energy electrons are also reduced.
[0042]
The conductivity and infrared absorption characteristics of the thin film of Examples deposited in this manner were measured. As a result, the film thickness was 210 nm, the photoconductivity / dark conductivity was 2 × 10 ⁶ , the SiH bond fraction was 10.2 atomic%, and the SiH ₂ bond fraction was 1.5 atomic%.
[0043]
(Production and physical properties of comparative examples)
In the comparative example, thin film deposition was performed under the same conditions as in the example except that quartz fine particles were not put into the plasma. As a result of measuring the conductivity and infrared absorption characteristics of the thin film of the comparative example, the film thickness was 300 nm, the photoconductivity / dark conductivity was 5 × 10 ⁵ , the SiH bond fraction was 10.3 atomic%, and the SiH ₂ bond content. The rate was 4.1 atomic%.
[0044]
(Comparison between Examples and Comparative Examples)
In the thin film of the example, the photoconductivity / dark conductivity increased about 4 times and the SiH ₂ bond fraction decreased to about 1 / 2.5 compared with the thin film of the comparative example. Therefore, it was confirmed that the structural and electrical properties of the thin film were improved by introducing quartz fine particles into the plasma. It was also confirmed that statistical heating of electrons near the plasma sheath was suppressed.
[0045]
It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0046]
【The invention's effect】
As described above, according to the present invention, in the capacitively coupled plasma source, generation of high energy electrons in the plasma can be suppressed and the electron energy can be controlled to be low, so that high quality thin film deposition and high precision etching can be performed. And the like, and the performance of solar cells, TFTs, and ICs can be improved. Moreover, since plasma processing can be performed in a large area, these can also be manufactured at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a plasma CVD apparatus used for thin film deposition in Examples and Comparative Examples.
FIG. 2 is a diagram showing a time change of plasma emission intensity in the vicinity of a plasma sheath in thin film deposition of an example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 Substrate, 12 Substrate holder, 13 Deposition chamber, 14 Anode electrode, 15 Cathode electrode, 16 High frequency power supply, 17 Alignment adjuster, 18 Input port, 19 Particle tank, 20 Gas introduction hole, 21 Gas exhaust hole, 22 Window, 23 , 24 Photodiode, 25 Current calculator, 26 Vibration generator, 27 Ring-shaped particulate collecting electrode.

Claims (8)

In the plasma processing method using a capacitively coupled plasma source, the electron energy and / or high energy electron density in the plasma center and the electron energy and / or high energy electron density in the vicinity of the plasma sheath are estimated, and the estimation is performed. Plasma in which the amount of statistical heating in the vicinity of the plasma sheath is reduced relative to the proportion of resistance heating in the center of the plasma by suspending the particles in the vicinity of the plasma sheath by introducing fine particles whose amount is controlled based on the plasma into the plasma. A plasma processing method comprising: performing plasma processing using a plasma, and removing the fine particles before or after the plasma processing is stopped.   2. The plasma processing method according to claim 1, wherein at least one kind of fine particles selected from the group consisting of resin, glass, Si polycrystal, carbon graphite, and diamond is used as the fine particles. 3. The plasma processing method according to claim 1, wherein the fine particles have a mass of 10 ⁻¹⁸ to 10 ⁻¹² g.   The plasma processing method according to claim 1, wherein a particle diameter of the fine particles is 0.01 to 1 μm. 5. The plasma processing method according to claim 1, wherein the electron energy and / or the high energy electron density is estimated based on a plasma emission amount. Means for generating plasma by a capacitively coupled plasma source, means for injecting fine particles into the plasma, means for estimating electron energy and / or high energy electron density in the center of the plasma, electron energy in the vicinity of the plasma sheath and / or Alternatively, a plasma processing apparatus comprising: means for estimating a high energy electron density; means for controlling a charged amount of fine particles based on the estimation; and means for removing fine particles. The means for estimating the electron energy and / or high energy electron density in the plasma center is a means for measuring the amount of plasma emission in the plasma center, and estimates the electron energy and / or high energy electron density in the vicinity of the plasma sheath. The plasma processing apparatus according to claim 6, wherein the means for measuring is means for measuring a plasma emission amount in the vicinity of the plasma sheath. The means for generating plasma by the capacitively coupled plasma source includes a pair of electrodes facing each other, and the means for removing the fine particles is provided between the electrodes. Plasma processing equipment.

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